It is known in the art to employ a refractory particulate-type casting core (e.g., a conventional sand foundry core) for forming an internal camshaft gallery within a cylinder block of an internal combustion engine cast within a mold. An example of such teaching is disclosed in the U.S. Pat. No. 2,783,510 to Dolza et al, granted Mar. 5, 1957. The camshaft gallery supports a camshaft of the engine for rotation within the cylinder block.
Accompanying the camshaft gallery in all known engines is one or more internal passageways for conducting lubricating oil to the rotating camshaft. Typically, these passageways take the form of a long and narrow oil gallery that extends along side the camshaft gallery and communicates therewith by a plurality of transverse feeder passages. With this type of system, the lubricating oil is introduced into the main oil gallery and then directed to various locations of the camshaft gallery of the feeder passages.
The known methods for forming such an oil gallery heretofore involve either drilling the gallery and feeder passages into the block or else casting the oil gallery in place during the manufacture of the block using specially designed cores and then drilling the feeder passages between the camshaft gallery and oil gallery. Both alternatives are costly and suffer from disadvantages as will be described below.
When drilling the oil gallery into the block, it is often necessary to drill the gallery from both ends. This double ended drilling process is necessary since the oil gallery extends virtually the entire length of the block and can not be practically formed by drilling from one end since the drilling tool has a tendency to wonder as it is extended further and further into the block. Double drilling adds to the cost of complexity of manufacturing the cylinder block. Another disadvantage is that the oil gallery passage is open at both ends of the block, thereby requiring one end be subsequently plugged. Such plugs are troublesome and over time have a tendency to loosen and leak.
Known specially manufactured cores include those disclosed in U.S. Pat. No. 2,991,520 to Dalton, granted Jul. 11, 1961; U.S. Pat. No. 3,945,429 to Wahlqvist, granted Mar. 23, 1976; and U.S. Pat. No. 4,829,642 to Thomas et al, granted May 16, 1989. The core of Thomas is of a cast-in stainless steel tube-type which remains in place with the cylinder block following casting. Such tubes, however, are problematic and that steps must be taken to assure that the outer surface is clean and free from any debris that would form imperfections in the casting or prevent good metal lay-up between the outside of the tube and the cylinder block metal. Such tubes thus add additional cost and complexity to the manufacturer of a cylinder block.
The Dalton and Wahlqvist cores are formed with a metal central support element surrounded by a sheath of refractory material, such as woven glass or particulate sand. These passageway cores are printed into the cavity walls of the mold so as to form a through-passage in both ends of the block, as with drilling, for supporting the cores in the mold cavity and accommodating removal of the cores following casting. These nonconventional cores add to the cost of manufacturing a block and have not enjoyed great commercial success. One open end of the through-passage also has to be plugged, as described previously with reference to drilled oil gallery passages and thus suffers from the same disadvantages.
Accordingly, there is a need in the industry for a suitable casting core for forming a long and narrow gallery passage within a cylinder block.